Ceramic dielectric composition

ABSTRACT

A ceramic dielectric compositon is provided which consists essentially of a sintered metal oxide mixture expressed by the formula:

This invention relates to a ceramic dielectric composition and more particularly to an improved ceramic dielectric composition, which is characterized by being sintered at a relatively low temperature, i.e., from approximately 700° C to approximately 900° C or so, exhibiting a dielectric constant varying linearly depending upon temperature variations over a wide use range, a reduced dielectric loss and enhanced resistivity and breakdown voltage. This ceramic dielectric composition is particularly suitable for "temperature-compensating" capacitors of a compact-type with large capacity such as laminar capacitors.

As ceramic dielectrics used in temperature-compensating capacitors, those which exhibit an enhanced dielectric constant, a reduced dielectric loss factor and a linear dependence of the dielectric constant upon temperature variations over a wide use range are required. Most ceramic dielectrics heretofore proposed for temperature-compensating capacitors contain as the basic ingredient titanium dioxide (TiO₂) such as SrTiO₃, CaTiO₃, MgTiO₃ or La₂ O₃.TiO₂. Suitable sintering temperatures of these ceramic dielectric compositions are generally 1,200° to 1,400° C.

Recently, a ceramic capacitor which is more compact and of more improved capacity and possesses a high reliability has been desired in the field including the communication industry. Thus, a capacitor of a thin ceramic film having 0.1 to 0.2 mm thickness and a ceramic laminar capacitor composed of a plurality of superimposed laminae each having a thickness of approximately 50 microns or less have been put to practical use.

However, such laminar ceramics of the known TiO₂ -base type are not satisfactory from the following points of view. First, since suitable sintering temperatures are high, the dielectric bodies are liable to be distorted and poor in yield. Second, laminar internal electrodes used in the laminar capacitor must be made of metals having a high melting point such as platinum or a platinum-palladium alloy and are, therefore, costly.

It is an object of the present invention to provide ceramic dielectric compositions having optimum sintering temperatures of approximately 600° to approximately 950° C, i.e. lower to a considerable extent than those of the known TiO₂ -base type dielectrics.

It is another object of the present invention to provide ceramic dielectric compositions having a dielectric constant varying linearly depending upon temperature variations over a broad use range.

It is still another object of the present invention to provide ceramic capacitors of enhanced reliability, i.e. improved insulation resistance and breakdown voltage.

It is a further object of the present invention to provide ceramic dielectric compositions particularly suitable for a temperature-compensating capacitor of a compact and laminar type.

Other objects and advantages will be apparent from the following description.

In accordance with the present invention, there is provided a ceramic dielectric composition consisting essentially of sintered metal oxide mixture expressed by the formula:

    [(Ba.sub.1.sub.-u Me.sub.u)O].sub.x.[(Ta.sub.1.sub.-v Nb.sub.v).sub.2 O.sub.5 ].sub.y.[Bi.sub.2 O.sub.3 ].sub.z

where Me is at least one divalent metal selected from the group consisting of lead and strontium, and x, y, z, u and v are numbers falling within the following ranges

    0.05 ≦ x ≦ 0.80,

    0.05 ≦ y ≦ 0.30,

    0.10 ≦ z ≦ 0.80,

    0 ≦ u ≦ 1.00,

    0 ≦ v ≦ 1.00 and

    x + y + z = 1.0.

If the ratio of x:y:z is 1:1:1 in the abovementioned formula, the ceramic dielectric composition is a ferroelectric substance which is popularly known as one of the Bi-Layer type dielectrics represented by the formula A² ⁺ Bi₂ R⁵ ⁺ O₉, where A² ⁺ and R⁵ ⁺ are divalent and pentavalent metals, respectively. It has been found that, when y of the above-mentioned formula falls within the range of approximately 0.30 to approximately 0.33, the ceramic dielectric composition is comprised of mixed crystals of a ferroelectric substance and a paraelectric substance. This ceramic dielectric composition is of little or no practical use because they exhibit large dielectric loss. Further, it has been found that, when y of the above-mentioned formula is not more than approximately 0.30, the ceramic dielectric composition is comprised of a single crystal and paraelectric, and the optimum sintering temperature is low, i.e. approximately 600° to approximately 950° C. From this finding, the ceramic dielectric composition of the invention has been completed.

When x of the above-mentioned formula is less than 0.05, variations in dielectric constant of the dielectrics depending upon temperature variations are non-linear. In contrast, when x exceeds 0.80, the dielectrics are poor in resistivity. Therefore, x should be within the range of 0.05 to 0.80, preferably 0.20 to 0.60.

The optimum sintering temperature of the dielectrics of the above-mentioned formula becomes low with a decrease of y. However, when y is too small, the dielectrics are poor in resistivity. In contrast, when y is too large, the dielectrics exhibit undesirably large dielectric loss. The range of y is from 0.05 to 0.30, preferably from 0.10 to 0.25. In such range, the dielectrics exhibit a resistivity of the order of 10¹³ to 10¹⁵ ohm-cm, which is far larger than those of the known TiO₂ -base type. This high resistivity results in enhancement in breakdown voltage. The dielectrics with y in the range of 0.05 to 0.30 possess a low sintering temperature of approximately 600° to approximately 950° C, and the permissible sintering temperature range is wide, i.e. approximately 50° to 100° C. Further, the dielectrics with y in the range of 0.05 to 0.30 exhibit a low dielectic loss factor of approximately 0.5 × 10.sup.⁻⁴ to approximately 12 × 10.sup.⁻⁴.

When z of the above-mentioned formula is less than 0.10, variations in dielectric constant depending upon temperature variations are non-linear. In contrast, when z is more than 0.80, the dielectrics are poor in sintering characteristics. The preferable range of z is from 0.20 to 0.65.

Both u and v of the above-mentioned formula may be varied within the range of 0 to 1.0. In other words, the ratio of BaO to PbO and/or SrO and the ratio of Ta₂ O₅ to Nb₂ O₅ may be optionally varied. When both u and v are zero, i.e. the dielectrics are of the formula; [BaO]_(x) . [Ta₂ O₅ ]_(y) . [Bi₂ O₃ ]_(z), and x, y and z are within the hereinbefore-mentioned ranges, the temperature coefficient of dielectric constant (ε.TC) is positive. However, the temperature coefficient of dielectric constant can be approximately zero or negative by partially substituting PbO and/or SrO for BaO and Nb₂ O₅ for Ta₂ O₅, respectively. Particularly, partial substitution of Nb₂ O₅ for Ta₂ O₅ reduces the dependence of the temperature coefficient ε.TC upon the variation in the ratio of BaO to PbO and/or SrO in the ingredient (Ba₁ _(-u) Me_(u))O, and therefore, results in dielectrics exhibiting a temperature coefficient ε.TC of approximately zero, even if the ratio of BaO to PbO and/or SrO is varied over a relatively broad range. For this advantage and the desired dielectric loss, preferable ranges of u and v are from 0.2 to 0.8 and from 0 to 0.6, respectively.

The ceramic dielectric composition of the invention may contain a minor amount of an additive metal oxide selected from titanium oxide, chromium oxide, molybdenum oxide and tungsten oxide. The ceramic dielectric composition having such an additive is advantageous over the fundamental dielectric composition of the hereinbefore-mentioned formula in that capacitors made of the former composition possess an improved load-durability of insulation resistance at a high temperature.

Laminar capacitors made of the fundamental dielectric composition having no additive exhibit an insulation resistance reduction to an extent such that, when they are continuously used at a temperature of 125° C and a voltage of 100V over a period of 1,000 hours, the initial insulation resistance on the order of 10¹³ ohm decreases to on the order of 10¹² ohm. In contrast, capacitors made of the dielectrics having the additive exhibit little or no reduction in the insulation resistance even after continuous use of 10,000 hours.

The amount of the additive is preferably not more than 4% by weight, more preferably within the range of 0.05% to 1% by weight, based on the weight of the fundamental dielectric composition of the hereinbefore-mentioned formula and expressed in terms of the amount of titanium dioxide (TiO₂), chromic oxide (Cr₂ O₃), molybdenum trioxide (MoO₃) and tungsten trioxide (WO₃), respectively. The load durability of insulation resistance is improved by the addition even in a trace amount, but becomes satisfactory by the addition of at least 0.05% by weight. When the amount of the additive is larger than 1% by weight, said load durability is approximately the same level, and when it exceeds 4% by weight, the optimum sintering temperature becomes undesirably high.

The above-mentioned additives may be used either alone or in combination. Of the additives, titanium oxide is most preferable because the resulting ceramic dielectrics consist of micro crystal grains.

The ceramic dielectric compositions of the present invention may be prepared as follows. Finely divided particles or powders of the respective metal oxides are blended with each other and shaped into a suitable form such as tablets. The shaped product is pre-sintered at a temperature of approximately 500° C to 800° C for 0.5 to 5 hours. The pre-sintered product is pulverized into fine particles or powders and shaped into a suitable form using or not using a binder. Then, the shaped product is sintered at a temperature of 600° C to 950° C for 0.5 to 8 hours. If desired, the aforesaid pre-sintering and the subsequent pulverization may be repeated prior to the sintering.

Instead of metal oxides, the respective metal compounds may be used which are in the form of carbonate salts, organic acid salts and hydroxides.

The invention is further disclosed in the following examples, which are illustrative but not limitative thereof. In the examples, percentages are by weight unless otherwise specified and asterisked specimen numbers in Tables I and II are comparative examples.

EXAMPLE 1

This example illustrates the fundamental ceramic dielectric compositions.

Using finely divided powders of barium monooxide (BaO), lead monooxide (PbO), strontium monooxide (SrO), tantalum pentoxide (Ta₂ O₅), niobium pentoxide (Nb₂ O₅) and bismuth trioxide (Bi₂ O₃), various ceramic dielectric compositions were prepared as follows.

The respective finely divided metal oxide powders were blended with each other and shaped into tablets. The tablets were presintered at a temperature of 500° to 800° C for 2 hours. The presintered tablets were pulverized into powders having a particle size of several microns by using a ball mill. After a binder was added to the powders, the powders were press-formed into discs having a diameter of 16 mm and a thickness of 1.0 mm. The discs were sintered at a temperature shown in Table I, below, for a period of one to two hours in an air atmosphere. Each disc was plated with a silver electrode, and its electrical and dielectric characteristics were tested. The test results and the compositions of the ceramic dielectrics are shown in Table I.

In Table I, double asterisked data in the column of ε.TC mean that variations in the dielectric constant depending upon temperature variations are not linear. Both dielectric constant and dielectric loss factor were measured at a frequency of 1 MHz.

                                      Table I                                      __________________________________________________________________________                                          Di-                                                                            electric  Resis-     Sintering            Spe-                                 con-      tivity     temper-              cimen              Ba.sub.1.sub.-u Me.sub.u                                                                   Ta.sub.1.sub.-v Nb.sub.v                                                             stant                                                                              Tan δ                                                                          (ohm-                                                                              ε.TC                                                                          ture                 No. X   Y   Z   U  Ba Pb Sr V  Ta Nb ε s                                                                        ×10.sup..sup.-4                                                                cm) (ppm/° C)                                                                      (°            __________________________________________________________________________                                                               C)                    1* 0.333                                                                              0.333                                                                              0.333                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  191 192   1×10.sup.13                                                                  **     1050                  2* 0.34                                                                               0.32                                                                               0.34                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  151 145   2×10.sup.14                                                                  **     1000                 3   0.35                                                                               0.30                                                                               0.35                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  82  1.0   1×10.sup.15                                                                  -215   910                  4   0.375                                                                              0.25                                                                               0.375                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  77  0.8   1×10.sup.15                                                                  -153   900                  5   0.40                                                                               0.20                                                                               0.40                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  75  0.7   2×10.sup.14                                                                  -143   850                  6   0.425                                                                              0.15                                                                               0.425                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  67  0.8   8×10.sup.13                                                                  -191   850                  7   0.45                                                                               0.10                                                                               0.45                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  71  1.3   8×10.sup.13                                                                  -177   830                  8   0.475                                                                              0.05                                                                               0.475                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  60  2.0   7×10.sup.12                                                                  -120   710                   9* 0.4875                                                                             0.025                                                                              0.4875                                                                             1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  56  2.0   3×10.sup.11                                                                  -110   600                  10  0.30                                                                               0.25                                                                               0.45                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  61  0.6   2×10.sup.13                                                                  -127   900                  11  0.20                                                                               0.25                                                                               0.55                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  62  0.8   5×10.sup.13                                                                  -123   900                  12  0.10                                                                               0.25                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  64  1.1   1×10.sup.13                                                                  -150   900                  13  0.30                                                                               0.20                                                                               0.50                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  75  1.5   2×10.sup.13                                                                  -112   870                   14*                                                                               0.025                                                                              0.25                                                                               0.725                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  66  8.3   4×10.sup.11                                                                  **     970                  15  0.25                                                                               0.10                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  62  2.4   3×10.sup.13                                                                  -65    830                  16  0.10                                                                               0.10                                                                               0.80                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  58  4.9   8×10.sup.12                                                                  +20    710                   17*                                                                               0.075                                                                              0.075                                                                              0.85                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  52  59    2×10.sup.10                                                                  +80    700                  18  0.45                                                                               0.25                                                                               0.30                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  56  2.2   3×10.sup.13                                                                  -171   900                  19  0.55                                                                               0.25                                                                               0.20                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  65  2.7   5×10.sup.13                                                                  -272   900                  20  0.55                                                                               0.30                                                                               0.15                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  72  2.7   3×10.sup.13                                                                  -314   930                   21*                                                                               0.55                                                                               0.325                                                                              0.125                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  120 200   1×10.sup.13                                                                  **     1050                 22  0.65                                                                               0.25                                                                               0.10                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  77  2.9   5×10.sup.13                                                                  -354   930                   23*                                                                               0.675                                                                              0.25                                                                               0.075                                                                              1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  124 10    2×10.sup.11                                                                  +1400  1050                 24  0.50                                                                               0.20                                                                               0.30                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  80  0.5   3×10.sup.13                                                                  -280   840                  25  0.60                                                                               0.10                                                                               0.30                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  70  1.2   2×10.sup.13                                                                  -150   830                  26  0.80                                                                               0.10                                                                               0.10                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  71  8.3   5×10.sup.13                                                                  -110   800                   27*                                                                               0.85                                                                               0.05                                                                               0.10                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  64  10.2  4×10.sup.11                                                                  -350   810                  28  0.65                                                                               0.05                                                                               0.30                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  52  9.1   1×10.sup.13                                                                  -170   710                  29  0.30                                                                               0.05                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  0  1.0                                                                               0  57  8.3   9×10.sup.12                                                                  -20    710                   30*                                                                               0.333                                                                              0.333                                                                              0.333                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               113 180   2×10.sup.13                                                                  **     1000                  31*                                                                               0.34                                                                               0.310                                                                              0.34                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               109 120   4×10.sup.13                                                                  **     975                  32  0.35                                                                               0.30                                                                               0.35                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               92  6.7   6×10.sup.14                                                                  -200   900                  33  0.37                                                                               0.26                                                                               0.37                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               74  5.0   2×10.sup.15                                                                  -219   850                  34  0.385                                                                              0.230                                                                              0.385                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               79  2.0   1×10.sup.15                                                                  -270   800                  35  0.40                                                                               0.20                                                                               0.40                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               72  0.8   4×10.sup.14                                                                  -245   775                  36  0.425                                                                              0.150                                                                              0.425                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               60  1.0   2×10.sup.14                                                                  -200   700                  37  0.45                                                                               0.10                                                                               0.45                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               45  1.3   2×10.sup.14                                                                  -190   650                  38  0.475                                                                              0.050                                                                              0.475                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               43  2.0   1×10.sup.13                                                                  -200   610                   39*                                                                               0.4875                                                                             0.025                                                                              0.4875                                                                             1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               40  5.0   2×10.sup.11                                                                  -140   --                   40  0.30                                                                               0.25                                                                               0.45                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               87  6.7   2×10.sup.14                                                                  -136   840                  41  0.225                                                                              0.250                                                                              0.625                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               91  7.7   1×10.sup.14                                                                  -101   840                  42  0.15                                                                               0.25                                                                               0.60                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               91  7.7   6×10.sup.13                                                                  -103   840                  43  0.05                                                                               0.30                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               74  10.0  4×10.sup.13                                                                  -74    870                  44  0.30                                                                               0.20                                                                               0.50                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               82  1.0   7×10.sup.14                                                                  -256   750                  45  0.15                                                                               0.20                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               76  2.0   2×10.sup.14                                                                  -27    750                  46  0.25                                                                               0.10                                                                               0.65                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               50  2.4   8×10.sup.13                                                                  -4     630                  47  0.10                                                                               0.10                                                                               0.80                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               46  3.3   1×10.sup.13                                                                  +15    600                   48*                                                                               0.025                                                                              0.175                                                                              0.80                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               44  5.0   2×10.sup.11                                                                  +30    710                   49*                                                                               0.075                                                                              0.075                                                                              0.85                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               43  6.7   2×10.sup.10                                                                  +75    600                   50*                                                                               0.50                                                                               0.35                                                                               0.15                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               120 240   2×10.sup.11                                                                  **     1140                 52  0.525                                                                              0.250                                                                              0.225                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               130 1.5   4×10.sup.14                                                                  -1110  900                  53  0.60                                                                               0.25                                                                               0.15                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               150 2.2   3×10.sup.14                                                                  -1200  870                   54*                                                                               0.65                                                                               0.30                                                                               0.05                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               210 300   8×10.sup.11                                                                  **     1100                 55  0.50                                                                               0.20                                                                               0.30                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               96  2.0   5×10.sup.14                                                                  -414   750                  56  0.65                                                                               0.20                                                                               0.15                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               152 2.6   5×10.sup.13                                                                  -805   810                  57  0.70                                                                               0.20                                                                               0.10                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               174 10.0  2×10.sup.13                                                                  -1100  770                  58  0.65                                                                               0.10                                                                               0.25                                                                               1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               70  3.1   1×10.sup.14                                                                  -540   710                   59*                                                                               0.825                                                                              0.050                                                                              0.125                                                                              1.0                                                                               0  1.0                                                                               0  1.0                                                                               0  1.0                                                                               52  12.5  3×10.sup.11                                                                  -300   810                   60*                                                                               0.333                                                                              0.333                                                                              0.333                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  290 1500  2×10.sup.13                                                                  **     1030                  61*                                                                               0.34                                                                               0.32                                                                               0.34                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  230 1000  4×10.sup.13                                                                  **     950                  62  0.35                                                                               0.30                                                                               0.35                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  92  9.1   2×10.sup.14                                                                  +45    920                  63  0.375                                                                              0.25                                                                               0.375                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  54  6.7   2×10.sup.14                                                                  +114   920                  64  0.40                                                                               0.20                                                                               0.40                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  46  5.0   2×10.sup.14                                                                  +147   850                  65  0.425                                                                              0.15                                                                               0.425                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  40  4.0   6×10.sup.14                                                                  +168   840                  66  0.45                                                                               0.10                                                                               0.45                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  37  5.0   6×10.sup.14                                                                  +174   800                  67  0.475                                                                              0.05                                                                               0.475                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  32  7.1   9×10.sup.13                                                                  +210   750                   68*                                                                               0.4875                                                                             0.025                                                                              0.4875                                                                             0  1.0                                                                               0  0  0  1.0                                                                               0  28  7.5   1×10.sup.11                                                                  +300   750                  69  0.30                                                                               0.25                                                                               0.45                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  58  4.8   4×10.sup.14                                                                  +104   930                  70  0.20                                                                               0.25                                                                               0.55                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  69  8.3   3×10.sup.14                                                                  +92    930                  71  0.10                                                                               0.25                                                                               0.65                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  82  125   2×10.sup.14                                                                  +40    930                  72  0.30                                                                               0.20                                                                               0.50                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  51  7.0   8×10.sup.14                                                                  +86    870                  73  0.05                                                                               0.25                                                                               0.70                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  49  4.0   2×10.sup.14                                                                  +90    870                  74  0.25                                                                               0.10                                                                               0.65                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  57  6.5   2×10.sup.14                                                                  +110   800                  75  0.10                                                                               0.10                                                                               0.80                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  63  9.6   5×10.sup.14                                                                  +214   870                   76*                                                                               0.075                                                                              0.075                                                                              0.85                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  72  1000  2×10.sup.14                                                                  **     840                  77  0.45                                                                               0.25                                                                               0.30                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  52  5.3   5×10.sup.14                                                                  +82    960                  78  0.55                                                                               0.25                                                                               0.20                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  44  10.0  3×10.sup.14                                                                  +140   930                  79  0.55                                                                               0.30                                                                               0.15                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  70  10.0  4×10.sup.14                                                                  +320   930                   80*                                                                               0.55                                                                               0.325                                                                              0.125                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  174 24.0  2×10.sup.14                                                                  **     1050                 81  0.65                                                                               0.25                                                                               0.10                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  32  10.5  4×10.sup.13                                                                  +155   930                   82*                                                                               0.675                                                                              0.25                                                                               0.075                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  44  450   2×10.sup.11                                                                  **     940                  83  0.50                                                                               0.20                                                                               0.30                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  39  6.7   4×10.sup.14                                                                  +167   870                  84  0.60                                                                               0.10                                                                               0.30                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  37  6.4   7×10.sup.14                                                                  +210   800                  85  0.80                                                                               0.10                                                                               0.10                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  35  10.0  2×10.sup.13                                                                  +267   870                   86*                                                                               0.85                                                                               0.05                                                                               0.10                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  30  14.0  4×10.sup.11                                                                  **     870                  87  0.65                                                                               0.05                                                                               0.30                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  32  8.1   7×10.sup.13                                                                  +270   830                  88  0.30                                                                               0.05                                                                               0.65                                                                               0  1.0                                                                               0  0  0  1.0                                                                               0  42  7.8   1×10.sup.14                                                                  +150   760                   89*                                                                               0.333                                                                              0.333                                                                              0.333                                                                              0  1.0                                                                               0  0  0  1.0                                                                               0  290 1500  2×10.sup.13                                                                  **     1030                 90  0.35                                                                               0.30                                                                               0.35                                                                               0.66                                                                              0.34                                                                              0.66                                                                              0  0  1.0                                                                               0  84  2.4   6×10.sup.14                                                                  ±0  910                  91  0.375                                                                              0.25                                                                               0.375                                                                              0.1                                                                               0.9                                                                               0.1                                                                               0  0  1.0                                                                               0  60  4.7   6×10.sup.14                                                                  +120   920                  92  0.375                                                                              0.25                                                                               0.375                                                                              0.4                                                                               0.6                                                                               0.4                                                                               0  0  1.0                                                                               0  71  2.1   6×10.sup.14                                                                  +8     920                  93  0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  0  1.0                                                                               0  75  1.2   1×10.sup.15                                                                  ±0  900                  94  0.375                                                                              0.25                                                                               0.375                                                                              0.7                                                                               0.3                                                                               0.7                                                                               0  0  1.0                                                                               0  76  1.0   7×10.sup.14                                                                  -7     900                  95  0.375                                                                              0.25                                                                               0.375                                                                              0.9                                                                               0.1                                                                               0.9                                                                               0  0  1.0                                                                               0  78  0.7   2×10.sup.14                                                                  -120   900                  96  0.375                                                                              0.25                                                                               0.375                                                                              0.1                                                                               0.9                                                                               0.05                                                                              0.05                                                                              0  1.0                                                                               0  60  4.2   3×10.sup.14                                                                  +95    900                  97  0.375                                                                              0.25                                                                               0.375                                                                              0.2                                                                               0.8                                                                               0.1                                                                               0.1                                                                               0  1.0                                                                               0  64  3.6   3×10.sup.14                                                                  +60    900                  98  0.375                                                                              0.25                                                                               0.375                                                                              0.2                                                                               0.8                                                                               0  0.2                                                                               0  1.0                                                                               0  64  8.9   3×10.sup.14                                                                  +67    940                  99  0.375                                                                              0.25                                                                               0.375                                                                              0.25                                                                              0.75                                                                              0  0.25                                                                              0  1.0                                                                               0  60  10.0  2×10.sup.14                                                                  +86    950                  100 0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  0.2                                                                               0.8                                                                               0.2                                                                               60  1.0   7×10.sup.14                                                                  ±0  840                  101 0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  0.4                                                                               0.6                                                                               0.4                                                                               64  1.0   7×10.sup.14                                                                  ±0  840                  102 0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  0.6                                                                               0.4                                                                               0.6                                                                               68  1.2   5×10.sup.14                                                                  -7     840                  103 0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  0.8                                                                               0.2                                                                               0.8                                                                               73  1.4   5×10.sup.14                                                                  -16    800                  104 0.375                                                                              0.25                                                                               0.375                                                                              0.2                                                                               0.8                                                                               0.2                                                                               0  0.5                                                                               0.5                                                                               0.5                                                                               67  1.0   3×10.sup.14                                                                  +4     840                  105 0.375                                                                              0.25                                                                               0.375                                                                              0.4                                                                               0.6                                                                               0.4                                                                               0  0.4                                                                               0.6                                                                               0.4                                                                               66  1.0   3×10.sup.14                                                                  ±0  840                  106 0.375                                                                              0.25                                                                               0.375                                                                              0.6                                                                               0.4                                                                               0.6                                                                               0  0.45                                                                              0.35                                                                              0.45                                                                              67  0.9   3×10.sup.14                                                                  ±0  840                  107 0.425                                                                              0.15                                                                               0.425                                                                              0.53                                                                              0.47                                                                              0.53                                                                              0  0  1.0                                                                               0  68  1.4   5×10.sup.14                                                                  ±0  840                  108 0.425                                                                              0.15                                                                               0.425                                                                              0.35                                                                              0.65                                                                              0.35                                                                              0  0.5                                                                               0.5                                                                               0.5                                                                               69  1.5   5×10.sup.14                                                                  ±0  790                  109 0.475                                                                              0.05                                                                               0.475                                                                              0.37                                                                              0.63                                                                              0.37                                                                              0  0  1.0                                                                               0  41  4.6   1×10.sup.14                                                                  ±0  710                  110 0.475                                                                              0.05                                                                               0.475                                                                              0.31                                                                              0.69                                                                              0.31                                                                              0  0.4                                                                               0.6                                                                               0.4                                                                               44  5.1   2×10.sup.14                                                                  ±0  700                  111 0.05                                                                               0.25                                                                               0.70                                                                               0.65                                                                              0.35                                                                              0.65                                                                              0  0  1.0                                                                               0  68  2.0   4×10.sup.13                                                                  ±0  870                  112 0.05                                                                               0.25                                                                               0.70                                                                               0.42                                                                              0.58                                                                              0.42                                                                              0  0.5                                                                               0.5                                                                               0.5                                                                               71  2.3   1×10.sup.14                                                                  ±0  810                  113 0.10                                                                               0.10                                                                               0.80                                                                               0.10                                                                              0.90                                                                              0.10                                                                              0  0  1.0                                                                               0  58  1.1   2×10.sup.14                                                                  ±0  870                  114 0.10                                                                               0.10                                                                               0.80                                                                               0.10                                                                              0.90                                                                              0.10                                                                              0  0.3                                                                               0.7                                                                               0.3                                                                               61  0.9   2×10.sup.14                                                                  ±0  820                  115 0.65                                                                               0.25                                                                               0.10                                                                               0.55                                                                              0.45                                                                              0.55                                                                              0  0  1.0                                                                               0  57  3.2   1×10.sup.13                                                                  ±0  930                  116 0.65                                                                               0.25                                                                               0.10                                                                               0.45                                                                              0.55                                                                              0.45                                                                              0  0.35                                                                              0.75                                                                              0.35                                                                              60  3.1   5×10.sup.14                                                                  ±0  870                  117 0.80                                                                               0.10                                                                               0.10                                                                               0.30                                                                              0.70                                                                              0.30                                                                              0  0  1.0                                                                               0  60  7.4   7×10.sup.13                                                                  ±0  840                  118 0.80                                                                               0.10                                                                               0.10                                                                               0.18                                                                              0.82                                                                              0.18                                                                              0  0.42                                                                              0.58                                                                              0.42                                                                              67  8.1   1×10.sup.14                                                                  ±0  810                  119 0.375                                                                              0.25                                                                               0.375                                                                              0.1                                                                               0.9                                                                               0.1                                                                               0  1.0                                                                               0  1.0                                                                               78  1.2   5×10.sup.14                                                                  -36    800                  120 0.375                                                                              0.25                                                                               0.375                                                                              0.58                                                                              0.42                                                                              0.58                                                                              0  1.0                                                                               0  1.0                                                                               80  1.1   5×10.sup.14                                                                  -32    800                  121 0.375                                                                              0.25                                                                               0.375                                                                              0.7                                                                               0.3                                                                               0.7                                                                               0  1.0                                                                               0  1.0                                                                               80  1.1   5×                                                                           -30sup.14                                                                             800                  122 0.375                                                                              0.25                                                                               0.375                                                                              1.0                                                                               0  0  1.0                                                                               0.6                                                                               0.4                                                                               0.6                                                                               60  12.5  2×10.sup.14                                                                  +100   950                  __________________________________________________________________________

EXAMPLE 2

This example illustrates electrical characteristics of laminar capacitors manufactured from the fundamental ceramic dielectric composition.

Layers of a fundamental ceramic dielectric composition prepared by the procedure set forth in Example 1, and of an internal electrode paste, the effective metal component of which was composed of only silver or of 70% of silver and 30% of gold, were superimposed alternately to form laminates. The laminates were heated at 500° C in an oxidative atmosphere, to burn out the organic materials, and then sintered at a temperature, shown in Table II below, for two hours. Each ceramic composition layer in the laminates had a thickness of 20 microns or 50 microns, as measured after the sintering. The laminates were fitted with external electrodes to form laminar capacitors. The laminar capacitors were tested for their insulation resistance and DC breakdown voltage (V_(BD)). Results are shown in Table II.

For comparison purposes, two known laminar capacitors were prepared, one of which was from a crystalline glass dielectric and a gold internal electrode, and another of which was from a TiO₂ -base type ceramic dielectric and an internal electrode composed of 70% of platinum and 30% of palladium, by the procedure set forth above. The two laminar capacitors were similarly tested for their electrical characteristics. Results were shown in Table II.

                                      Table II                                     __________________________________________________________________________     Thickness of                                                                   ceramics   50 microns 20 microns                                               Characteristics                                                                           Insulation Insulation                                                                               Composition                                                                           Sintering                               Dielectric resistance                                                                           V.sub.BD                                                                            resistance                                                                          V.sub.BD                                                                            of     temperature                             materials  (ohm) (V)  (ohm)                                                                               (V)  electrode                                                                             (° C)                            __________________________________________________________________________                2×10.sup.13                                                                    2,000                                                                               2×10.sup.12                                                                   1,100                                                                               Ag     870                                     Specimen No. 5                                                                            2×10.sup.13                                                                    2,000                                                                               2×10.sup.12                                                                   1,150                                                                               Ag:70  870                                                                     Au:30                                                     2×10.sup.13                                                                    2,100                                                                               5×10.sup.12                                                                   1,300                                                                               Ag     800                                     Specimen No. 34                                                                           2×10.sup.13                                                                    2,100                                                                               5×10.sup.12                                                                   1,300                                                                               Ag:70  800                                                                     Au:30                                                     2×10.sup.13                                                                    1,500                                                                               5×10.sup.12                                                                    900 Ag     850                                     Specimen No. 64                                                                           2×10.sup.13                                                                    1,500                                                                               5×10.sup.12                                                                    900 Ag:70  850                                                                     Au:30                                                     2×10.sup.13                                                                    2,100                                                                               1×10.sup.13                                                                   1,300                                                                               Ag     840                                     Specimen No. 101                                                                          2×10.sup.13                                                                    2,100                                                                               1×10.sup.13                                                                   1,300                                                                               Ag:70  840                                                                     Au:30                                          Crystalline galss*                                                                        1.3×10.sup.13                                                                  1,000                                                                               --   --   Au     1,000                                   TiO.sub.2 base type*                                                                      4.0×10.sup.12                                                                   700 --   --   Pt:70  1,300                                                                   Pd:30                                          ceramics                                                                       __________________________________________________________________________      *Comparative examples                                                    

Further, it was proved that the variations of electrostatic capacity of capacitors (specimen Nos. 5, 34, 64 and 101) depending upon the temperature variations were linear over the temperature range from -55° C to +125° C, and their temperature coefficients were -143 ppm/° C, -270 ppm/° C, +147 ppm/° C and approximately zero ppm/° C, respectively. These features are similar to ε.TC shown in Table I.

Although gold, platinum or a platinum-palladium alloy had to be used as the internal electrode in a known ceramic laminar capacitor, it was proved that silver or silver alloys composed of a predominant amount of silver and a minor amount of platinum or palladium might be advantageously used in ceramic laminar capacitors prepared from the dielectric composition of the invention.

EXAMPLE 3

This example illustrates the effect brought about by the addition of the additives.

Laminar capacitors were prepared by the general procedure set forth in Example 2, wherein an internal electrode of silver was used and each ceramic layer in the laminates had a thickness of 20 microns. Each laminar capacitor was tested for its load-durability of insulation resistance by applying a voltage of 100 volts at 125° C. Results are shown in Table III, in which the load-durability is expressed in terms of the period (IR reduction period) during which the insulation resistance reduces to one tenth of the original value.

                  Table III                                                        ______________________________________                                                                       Amount IR                                               Fundamental            of     reduction                                 Specimen                                                                              composition            additive                                                                              period                                    No.    (Specimen No.)                                                                               Additive (%)    (hr)                                      ______________________________________                                         123    3             TiO.sub.2                                                                               0.3    >10,000                                   124    8             TiO.sub.2                                                                               0.3    >10,000                                   125    16            TiO.sub.2                                                                               0.3    >10,000                                   126    22            TiO.sub.2                                                                               0.3    >10,000                                   127    32            TiO.sub.2                                                                               0.3    >10,000                                   128    38            TiO.sub.2                                                                               0.3    >10,000                                   129    43            TiO.sub.2                                                                               0.3    >10,000                                   130    57            TiO.sub.2                                                                               0.3    >10,000                                   131    62            TiO.sub.2                                                                               0.3    >10,000                                   132    63            TiO.sub.2                                                                               0.3    >10,000                                   133    67            TiO.sub.2                                                                               0.3    >10,000                                   134    75            TiO.sub.2                                                                               0.3    >10,000                                   135    81            TiO.sub.2                                                                               0.3    >10,000                                   90     90            --       --     1,000                                     136    90            TiO.sub.2                                                                               0.05   4,000                                     137    90            TiO.sub.2                                                                               0.1    >10,000                                   138    90            TiO.sub.2                                                                               0.3    >10,000                                   139    90            TiO.sub.2                                                                               0.5    >10,000                                   140    90            TiO.sub.2                                                                               1.0    >10,000                                   141    90            TiO.sub.2                                                                               4.0    >10,000                                   142    90            Cr.sub.2 O.sub.3                                                                        0.3    >10,000                                   143    90            MoO.sub.3                                                                               0.3    >10,000                                   144    90            WO.sub.3 0.3    >10,000                                   145    90            TiO.sub. 2                                                                              0.2    >10,000                                                        Cr.sub.2 O.sub.3                                                                        0.2                                              146    90            MoO.sub.3                                                                               0.5    >10,000                                                        WO.sub.3 0.5                                              147    90            TiO.sub.2                                                                               0.5    >10,000                                                        MoO.sub.3                                                                               0.5                                              148    90            Cr.sub.2 O.sub.3                                                                        0.4    >10,000                                                        MoO.sub.3                                                                               0.4                                              149    90            TiO.sub.2                                                                               0.5    >10,000                                                        WO.sub.3 0.5                                              97     97            --       --     1,000                                     150    97            TiO.sub.2                                                                               0.3    >10,000                                   102    102           --       --     1,000                                     151    102           TiO.sub.2                                                                               0.3    >10,000                                   122    122           --       --     1,000                                     152    122           TiO.sub.2                                                                               0.3    >10,000                                   105    105           --       --     1,000                                     153    105           TiO.sub.2                                                                               0.3    >10,000                                   120    120           --       --     1,000                                     154    120           TiO.sub.2                                                                               0.3    >10,000                                   155    120           TiO.sub.2                                                                               1.0    >10,000                                   156    120           TiO.sub.2                                                                               4.0    >10,000                                   101    101           --       --     1,000                                     157    101           Cr.sub.2 O.sub.3                                                                        0.05   4,000                                     158    101           Cr.sub.2 O.sub.3                                                                        0.10   >10,000                                   159    101           Cr.sub.2 O.sub.3                                                                        1.0    >10,000                                   160    101           Cr.sub.2 O.sub.3                                                                        4.0    >10,000                                   161    101           MoO.sub.3                                                                               1.0    >10,000                                   162    101           WO.sub.3 1.0    > 10,000                                  163    101           WO.sub.3 4.0    >10,000                                   164    101           MoO.sub.3                                                                               0.5    >10,000                                                        WO.sub.3 0.5                                              165    101           MoO.sub.3                                                                               0.5    >10,000                                                        Cr.sub.2 O.sub.3                                                                        0.5                                              ______________________________________                                     

What we claim is:
 1. A ceramic dielectric composition consisting essentially of sintered metal oxide mixture expressed by the formula:

    [(Ba.sub.1.sub.-u Me.sub.u)O].sub.x . [(Ta.sub.1.sub.-v Nb.sub.v).sub.2 O.sub.5 ].sub.y . ]Bi.sub.2 O.sub.3 ].sub.z

where Me is at least one divalent metal selected from the group consisting of lead and strontium, and x, y, z, u and v are numbers falling within the following ranges

    0.05 ≦ x ≦ 0.80,

    0.05 ≦ y ≦ 0.30,

    0.10 ≦ z ≦ 0.80,

    0 ≦ u ≦ 1.00,

    0 ≦ v ≦ 1.00 and

    x + y + z = 1.0


2. The ceramic dielectric composition according to claim 1 wherein x is a positive number falling within the range of 0.20 to 0.60.
 3. The ceramic dielectric composition according to claim 1 wherein y is a positive number falling within the range of 0.10 to 0.25.
 4. The ceramic dielectric composition according to claim 1 wherein z is a positive number falling within the range of 0.20 to 0.65.
 5. The ceramic dielectric composition according to claim 1 wherein u is a positive number falling within the range of 0.2 to 0.8.
 6. The ceramic dielectric composition according to claim 1 wherein v is a number falling within the range of 0 to 0.6.
 7. The ceramic dielectric composition according to claim 1 which further comprises at least one metal oxide selected from the group consisting of oxides of titanium, chromium, molybdenum and tungsten in an amount of not larger than 4.0% by weight based on the weight of the ceramic dielectric composition of said formula and expressed in terms of the amount of titanium dioxide (TiO₂), chromic oxide (Cr₂ O₃), molybdenum trioxide (MoO₃) and tungsten trioxide (WO₃), respectively.
 8. The ceramic dielectric composition according to claim 7 wherein the amount of said metal oxide is 0.05% to 1.0% by weight.
 9. The ceramic dielectric composition according to claim 7 wherein said metal oxide is titanium oxide. 